The present invention relates to projection systems. More particularly, some embodiments of the present invention relate to a projection system having uniform, bright, homogenized output.
Projection systems have been known for some time. Cinema projectors until recently have all been based on analog technology. Historically, Thomas Edison invented a device called the “kinescope”, which passed a light through a transparent medium. This device used an electric arc lamp to produce the light required for projection. Because of the size of the arc gap, significant amounts of light were lost and only a very small percentage was usable for the projected image. Modern advancements were mostly mechanical in nature, the film was perforated, mechanisms were designed to carry the film reel in front of the light etc . . . . The nature of the light source, however, did not change until the invention of the Xenon bulb, which is a high pressure glass container with the electrodes inside the glass cavity. Xenon bulbs for cinema today vary in watts depending on the screen size. They range from 2500 watts to 15,000 watts. Their efficiency was greater than the metallic arc lamps as well as a longer life, sometimes as long as 1000 hours. But like the metallic arc, the gap between the electrodes is still quiet wide at 7 to 10 mm. This gap is especially important when one is using a small (less than an inch) imager. The physical principle that limits the amount of usable light is the “optical invariant” or “etendu”, which is based on the acceptance angle of the arc gap/reflector relationship to the image plane. The smaller the gap the more light can be captured for the projection imager. All the current digital cinema projectors (TI, JVC, Kodak) use this approach with the xenon arc lamp reflector combination. Unfortunately they cannot over come the optical invariant and like the original Edison metallic arc and lose a significant portion of the usable light. Frequently, these systems are unable to provide a uniform, bright, homogenized output. Such a system remains wanting.
Projection systems using LCD image panels are at a further disadvantage since the LCD panel polarizes light and in do so, rejects 50% of the light that are at the wrong polarization. So immediately, those LCD panels are only half as bright as other image panels and have an additional hurdle to overcome.